Nanostructural analysis of therapeutic ultrasound effect on rat tendon healing process

Abstract

Therapeutic pulsed ultrasound (TPUS) is one among several therapies used to promote tissue repair. This study assessed the effect of TPUS at two different intensities on rat Achilles tendon's microstructure. Twenty four male adult Wistar rats (aged 6 months) were submitted to right calcanean tendon radical tenotomy, with no ensuing tendon suture, and divided into four groups: control group (GC) did not receive any treatment; group 1 (G1) was treated with 20%, 1 MHz TPUS at 0.3 W/cm²;, with effective radiation area of 1,0 cm²; group 2 (G2) was treated with same parameter TPUS, but at 1.5 W/cm² intensity; group 3 (G3) received simulated treatment (equipment off). In all three groups, treatment consisted of one daily 5-minute session, for ten days. On the 11th post-operative day animals were euthanized and their tendons removed for qualitative and quantitative analysis by polarized light microscopy (PLM), light microscopy (LM), and atomic force microscopy (AFM). Both PLM and AFM analysis results showed better collagen fibre organization, aggregation and orientation at G1. The quantitative analysis of fibroblasts (mean 400.7 fibroblast/field) and capillary vessels (mean 2.22 vessels/field) through LM showed no statistically significant differences between groups (p>;0.05). It may hence be said that the process of tendon regeneration in adult rats may benefit from treatment with TPUS at low intensity.